[Fix #912] Enhance Rails/Delegate by adding delegation detection for self.class, constants, class variables, global variables, and instance variables

[ydakuka]

Fix #912

---

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[koic]

That's my two cents. Can you tweak the example? e.g.,

Suggested change

	@inst_obj.foo
	end
	RUBY
	expect_correction(<<~RUBY)
	delegate :foo, to: :@inst_obj
	@instance_variable.foo
	end
	RUBY
	expect_correction(<<~RUBY)
	delegate :foo, to: :@instance_variable

[koic]

Suggested change

	@@cls_obj.foo
	end
	RUBY
	expect_correction(<<~RUBY)
	delegate :foo, to: :@@cls_obj
	@@class_variable.foo
	end
	RUBY
	expect_correction(<<~RUBY)
	delegate :foo, to: :@@class_variable

[koic]

It's a corner case, but wouldn't it be possible to apply the same handling to global variables as well?

[ydakuka]

It's a corner case, but wouldn't it be possible to apply the same handling to global variables as well?

I'm not sure if Rails delegate supports it because I couldn't find an example of it in the official documentation.
https://api.rubyonrails.org/classes/Module.html#method-i-delegate
Ok, I'll check.

[koic]

This is the behavior in Rails 8.0.1. For your reference.

$ bin/rails -v
Rails 8.0.1

$ cat /tmp/x.rb
class X
  def foo
    puts 'hi'
  end
end

$global_variable = X.new

class Y
  delegate :foo, to: :$global_variable
end

Y.new.foo

$ bin/rails r /tmp/x.rb
hi

[ydakuka]

Thank you, I've fixed it.

[koic]

Can you add a mention of global variables?

[ydakuka]

Done.

P.S. I got a failed test that is not related to this PR.

[koic]

The issue was fixed in f9adec0. There's no problem with this PR. Thank you!

[koic]

Thanks!